Optical clock intercomparison with $6\times 10^{-19}$ precision in one hour

TL;DR

This paper demonstrates an optical clock intercomparison achieving a record fractional frequency stability of 6×10⁻¹⁹ in one hour, enabling highly precise measurements relevant to quantum sensing and fundamental physics.

Contribution

Utilizing ultrastable cryogenic silicon cavity lasers and advanced frequency combs, the study achieves unprecedented clock stability and precision in optical lattice clocks.

Findings

Achieved fractional instability of 4.8×10⁻¹⁷/√τ with anti-synchronous comparison.

Revealed quantum projection noise limited instability of 3.5(2)×10⁻¹⁷/√τ.

Achieved a measurement precision of 5.8(3)×10⁻¹⁹ after one hour.

Abstract

Improvements in atom-light coherence are foundational to progress in quantum information science, quantum optics, and precision metrology. Optical atomic clocks require local oscillators with exceptional optical coherence due to the challenge of performing spectroscopy on their ultra-narrow linewidth clock transitions. Advances in laser stabilization have thus enabled rapid progress in clock precision. A new class of ultrastable lasers based on cryogenic silicon reference cavities has recently demonstrated the longest optical coherence times to date. In this work we utilize such a local oscillator, along with a state-of-the-art frequency comb for coherence transfer, with two Sr optical lattice clocks to achieve an unprecedented level of clock stability. Through an anti-synchronous comparison, the fractional instability of both clocks is assessed to be $4.8\times 10^{-17}/\sqrt{\tau}$ for an averaging time $\tau$ in seconds. Synchronous interrogation reveals a quantum projection noise dominated instability of $3.5(2)\times10^{-17}/\sqrt{\tau}$, resulting in a precision of $5.8(3)\times 10^{-19}$ after a single hour of averaging. The ability to measure sub-$10^{-18}$ level frequency shifts in such short timescales will impact a wide range of applications for clocks in quantum sensing and fundamental physics. For example, this precision allows one to resolve the gravitational red shift from a 1 cm elevation change in only 20 minutes.